arXiv subjects

Won Bo Lee

Publications and source records attributed to Won Bo Lee.

22 records · Page 2Linked to original sources

arXiv2018

"Two-phase" thermodynamics of the Frenkel line

The Frenkel line, a crossover line between rigid and nonrigid dynamics of fluid particles, has recently been the subject of intense debate regarding its relevance as a partitioning line of supercritical phase, where the main criticism comes from the theoretical treatment of collective particle dynamics. From an independent point of view, this Letter suggests that the two-phase thermodynamics model may alleviate this contentious situation. The model offers new criteria for defining the Frenkel line in the supercritical region and builds a robust connection among the preexisting, seemingly inconsistent definitions. In addition, one of the dynamic criteria locates the rigid-nonrigid transition of the soft-sphere and the hard-sphere models. Hence, we suggest the Frenkel line be considered as a dynamic rigid-nonrigid fluid boundary, without any relation to gas-liquid transition. These findings provide an integrative viewpoint combining fragmentized definitions of the Frenkel line, allowing future studies to be carried out in a more reliable manner.

cond-mat.stat-mech↗

arXiv2018

Widom delta of supercritical gas-liquid coexistence

We report on the coexistence of liquid-like and gas-like structures in supercritical fluid (SCF). The deltoid coexistence region encloses the Widom line, and may therefore be termed the "Widom delta". Machine learning analysis of simulation data shows continuous transition across the delta, from liquid-like to gas-like states, with fractions following a simplified two-state model. This suggests a microscopic view of the SCF as a mixture of liquid-like and gas-like structures, where the anomalous behavior near the critical point originates from fluctuations between the two types.

cond-mat.stat-mech↗

arXiv2011

Molecular Dynamics Simulation Study of Nonconcatenated Ring Polymers in a Melt: I. Statics

Molecular dynamics simulations were conducted to investigate the structural properties of melts of nonconcatenated ring polymers and compared to melts of linear polymers. The longest rings were composed of N=1600 monomers per chain which corresponds to roughly 57 entanglement lengths for comparable linear polymers. For the rings, the radius of gyration squared was found to scale as N to the 4/5 power for an intermediate regime and N to the 2/3 power for the larger rings indicating an overall conformation of a crumpled globule. However, almost all beads of the rings are "surface beads" interacting with beads of other rings, a result also in agreement with a primitive path analysis performed in the following paper (DOI: 10.1063/1.3587138). Details of the internal conformational properties of the ring and linear polymers as well as their packing are analyzed and compared to current theoretical models.

cond-mat.soft↗

arXiv2011

Molecular Dynamics Simulation Study of Nonconcatenated Ring Polymers in a Melt: II. Dynamics

Molecular dynamics simulations were conducted to investigate the dynamic properties of melts of nonconcatenated ring polymers and compared to melts of linear polymers. The longest rings were composed of N=1600 monomers per chain which corresponds to roughly 57 entanglement lengths for comparable linear polymers. The ring melts were found to diffuse faster than their linear counterparts, with the self-diffusion coefficient for both architectures scaling as approximately N to the -2.4 power for large N. The mean-square displacement of the center-of-mass of the rings follows a sub-diffusive behavior for times and distances beyond the mean-square gyration radius, neither compatible with the Rouse nor the reptation model. The rings relax stress much faster than linear polymers and the zero-shear viscosity was found to vary as approximately N to the 1.4 power which is much weaker than the N to the 3.4 power of linear chains, not matching any commonly known model for polymer dynamics when compared to the observed mean-square displacements. These findings are discussed in view of the conformational properties of the rings presented in the preceding paper (DOI: 10.1063/1.3587137).

cond-mat.soft↗